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Full text of "Diseases Of The Nose Throat And Ear"

258

THE EAR

The essential part of the inner ear is the membranous labyrinth, developed
from an ingrowth of cephalic ectoderm called the otic vesicle, which later
differentiates into two parts (Fig. 141): (1) the pars superior or static labyrinth
consists of the utricle and three semicircular canals. This part contains the
balance mechanism and is connected with the vestibular nerve, and (2) the

5l* 138* Serai-diagrammatic representation of
«« membranous labyrinth, viewed from with-
?S1" ?' Membranous cochlea; 2, Saccule; 3,
!^£ICie;.4* Crus «™urae; 5, Saccus endo-
lymphafacus; 6 and 7, Fine ducts from utricle
!X *-Sac?jJe which l°in to form the endolym-
Phatic duct; 8, Canalis reuniens, connecting
intravestibular part of the cochlear duct with
the saccule.

labyrinth opened up and
.         <»*•   I.   Helicotmna;   2,

spbencus for saccule; 3, Crista
Recesses elHpticus for utricle??
^                             vestibule; 6,

•

£^«Ste£<^^w£rcSlea7;
?£S™S <* I»Syini>tiatic aquedua; », Ai«f§f

ST^J£T«L£«*5>* .W* °f

and scala v^stibuli of

«f C?9aei-<Afoto:     ** <

9 and Id is the bony spiral

Fig. 139. Bony labyrinth of left side, viewed
from without. 1, Bony cochlea; 2, Fenestra
vestibuli (oval window); 3, Ampulla of lateral
(horizontal) semicircular canal; 4, Ampulla of
superior vertical canal; 5, Convexity of superior
canal; 6, Crus commune; 7, Convexity of
posterior vertical canal; 8, Convexity of lateral
canal; 9, Ampulla of posterior vertical canal;
10, Fenestra cochleae (round window).

Fig. 141. Diagram showing transverse i
section through head of fetus at an early s
of development, and indicating the dev<_

ment  of the external   acoustic  mcatus,__„

middle ear cteft, and the labyrinth. 1, Primitive
ductus endolymphaticus; 2, Primitive static
labyrinth (utricle and canals); 3, Primitive
auditory labyrinth (saccule and cochlea); 4,
Primitive tympanic cavity; 5, External acoustic
raeatus; 6, Pharyngotympanic (Eustachian)
tube; 7, Pharynx; 8, Notochord.

Pars inferior or auditory labyrinth consisting of the saccule and membranous

or cochlear duct containing the hearing mechanism is connected
with the cochlear nerve.

^^ labyrinth. In the early embryo the membranous labyrinth sinks
se surrounding mesoderm which is converted into layers of cartilage